The synaptic membrane protein syntaxin mediates specific docking and fusion of synaptic vesicles with synaptic membranes. The cytoplasmic portion of syntaxin contains a domain responsible for specific recognition of cognate molecules on synaptic vesicles, and other domains that serve to regulate its function. Crystals of each of these regions have been prepared from protein expressed in E. coli, and we propose to determine their structures by MAD phasing of the selenomethionyl proteins, using the tunable 1-5 AD beamline for data collection.